Purified testosterone-estradiol binding globulins (TEBG) of human and bovine plasma, both the native and desialylated proteins, will be examined by isolectric focusing and their interactions with plasma membranes studied. The kinetics of dissociation and association of steroids with these TEBG samples will be measured and the role of this protein in modulating access of steroids to hormone-sensitive tissues evaluated. These events will be studied with available human and bovine samples of different ages.